The present invention relates to location determination and, in particular, to location determination by an entity in an environment in which multiple items of location data are diffused to and between entities by short-range communication.
A number of technologies exist for the short range communication of information between mobile devices. These technologies include infra-red based technologies and low-power radio technologies (including, in particular, the recent xe2x80x9cBluetoothxe2x80x9d short range wireless standard). Depending on the technology implementation, differing types of message propagation will be enabled including asynchronous message broadcast, and multicast and point-to-point duplex connections established after coordination and negotiation between communicating devices.
One possible use for such short-range technologies is the transmission of local information to passers-by equipped with mobile devices having short-range transceivers, the local information being, for example, transmitted by a shop to inform the passers-by of current promotions. Another use is in location beacons that transmit location information to passers-by.
It is known, for example from EP-A-0,948,222, to diffuse information amongst users by short range wireless links so that a user need not be in range of an originating transmitter in order to receive the information sent out by the latter. Such an arrangement is likely to be particularly useful in environments such as shopping malls, city centers, tourist attractions, theme parks or any other location where large numbers of users carrying mobile devices with short-range transceivers are likely to be in one locality. Another important area of application is the diffusion of information between devices fixed in cars.
FIG. 1 of the accompanying drawings depicts an information diffusion process in which an originating information point 10 (typically fixed, but not necessarily so) sends out the information over a short-range radio link to nearby mobile devices, in this case device 11. The receiving device 11 transmits on the information to a neighboring device 12 and then moves (see dashed arrow in FIG. 1) before sending on the information again to another device 14. Meanwhile mobile device 12 has moved into proximity with device 13 to which it also transmit the information. Device 13 now moves near to the device 14 and passes the latter the informationxe2x80x94however, as device 14 already has the information from device 11, it ignores the copy from device 13. Device 13 also passes the information to a fixed relay transceiver which subsequently passes the information to a mobile device 15. Finally, device 15 passes the information to device 14 which has now within range of device 15; again, device 14 ignores the copy information from device 15.
It can be seen that information can be rapidly diffused among the population of mobile-device users in the general vicinity of the source 10. So, the process of diffusion takes advantage of both the short range wireless technology and the movement of the users carrying the devices.
By applying appropriate diffusion-limiting mechanisms (for example, by assigning the original information a total time to live of, for example, 10 minutes), the information can be restricted to the vicinity of the originating point 10. This makes the diffusion process appropriate for the diffusion of location relevant information that is primarily of use only in the vicinity of point 10.
The diffused information can, of course, include the location of the originating point. For devices receiving the information directly from the originating point, this provides them with a fairly accurate indication of their location (because the information is received over a short-range link). However, as the information is diffused between devices, the newly-receiving devices get less and less accurate location information.
Our European Application EP-A-1 133 115 describes a method by which an entity receiving location data by diffusion from several different sources, can use this data to estimate its current position in dependence on the relative prominence of the sources.
Our co-pending European Application EP-A-1 174 728 describes another method by which an entity can discover its location using multiple items of location data received by short-range diffusion from several sources. In this method, each location data item includes an indication of the distance traveled by the location data item from its source, either by displacement of entities temporarily holding the item or by transmission. This distance represents an upper bound on the current distance of a receiving entity from the source concerned and this can be used, together with upper-bound distances from other sources, to discover a current zone where the entity is likely to be located; various averaging techniques can then be applied to derive a current location for the entity.
This latter method can involve significant processing of the received location data which may not always be desirable.
It is an object of the present invention to provide a location discovery method and apparatus that uses location data items including both source-location and distance-from-source data which, at least in certain embodiments, involves reduced processing of the location data.
According to one aspect of the present invention, there is provided a location determination method wherein an entity receives, by short-range communication, location data items originating at known locations, each location data item including a displacement value indicative of the displacement of the item since leaving a specified said known location; the entity deriving its location from location data items it has received by effecting a weighted combination of the known locations specified in the received location data items, the weighting of the known location specified in each received location data item being dependent on the associated displacement value.
According to another aspect of the present invention, there is provided a location determination method wherein location data items originating at known locations are passed to, and diffused between, entities by short-range communication, each location data item received by an entity indicating a separation distance of the entity from a specified said known location; a said entity deriving its location from location data items it has received by combining the known locations specified in the location data items in dependence on the related separation distances and/or the ages of the location data items.
According to a further aspect of the present invention, there is provided a mobile entity provided with a location determination system comprising:
a short-range receiver for receiving location data items from currently nearby transmitting entities, each location data item indicating a displacement value of the entity from a specified known location;
a memory for storing the received data items;
a distance sub-system for measuring or estimating the distance travelled by the mobile entity;
an update arrangement for updating the received data items by increasing the displacement value associated with each data item by the distance measured or estimated by the distance sub-system since the item concerned was received or last updated; and
a location derivation arrangement operative to determine the location of the entity by effecting a weighted combination of the known locations specified in the received location data items, the weighting of the known location specified in each received location data item being dependent on the associated displacement value.
According to a still further aspect of the present invention, there is provided a mobile entity provided with a location determination system comprising:
a short-range receiver for receiving location data items from currently nearby transmitting entities, each location data item indicating a displacement value of the entity from a specified known location;
a memory for storing the received data items;
a distance sub-system for measuring or estimating the distance travelled by the mobile entity;
an update arrangement for updating the received data items by increasing the displacement value associated with each data item by the distance measured or estimated by the distance sub-system since the item concerned was received or last updated; and
a location derivation arrangement operative to determine the location of the entity by effecting a weighted combination of the known locations specified in the received location data items, the weighting of the known location specified in each received location data item being dependent on the associated displacement value.